gRFC L76: Break 2.7 Deprecate gevent Support - Python Major Version Bump

[Lidi Zheng]

Hi,

This propose suggests gRPC Python should perform a major version bump to achieve two following goals:

1. Stop releasing 2.7 binaries and stop coding in Python 2/3 compatible manner;
2. Drop custom IO manager usages (e.g., gevent), which will be re-implemented via EventEngine API in the future.

GitHub Issue: https://github.com/grpc/proposal/pull/217

gRFC: https://github.com/lidizheng/proposal/blob/l76-python-major-version/L76-python-major-version-bump.md

Comments/suggestions are welcomed!

Lidi Zheng

[Lidi Zheng]

Correct GitHub Issue link: https://github.com/grpc/proposal/pull/217